Ultra high frequency control system



Jan- 7, 1947- M. D. FlsKE ETAL '2,413,963

ULTRA HIGH FREQUENCY CONTROL SYSTEM Filed Sept. 17, 1942 Their Attorneg.

Patented Jan., 7, 1947 ULTRA HIGH FREQUENCY CONTROL l STEM v Milan n. Fiske and Chauncey G. suits. sche'- nectady, N. Y., assignors to General Electric Company, a corporation of New :York

'Application Septemberl7, 1942, Serial No. 458,670

A Our -invention relates to ultra high frequency control systems and more particularly to systems for controlling the propagation of electromagnetic waves through dielectric wave guides of the hollow-pipe type.

It has been appreciated for some timethat It is' a still further object of our invention to I'provide new and improved ,apparatus including controlled space charge regions'associated with ultra high frequency electromagnetic waves may 1 be transmitted through dielectric wave guides of the hollow-pipe type if the electromagnetic waves are of a frequency greater than the critical or minimum frequency established by the dimensions of the wave guide, particularly the` transverse dimensions.

The types of waves which may -be transmitted dielectrically through guides of this nature are great in' number and have heretofore been" classified generally into the E and H types. In the E type wave, the electromagnetic waves have both longitudinal and transverse components of electric eld, but` only a transverse component of magnetic field. A4By the use of ,the word transverse is meant transverse to guide. In the I-I type of wave, the electromagnetic waves have both longitudinal and transthe direction of wave propagation through the a tuned aperture or slot positionedl in the dielectric wave guide whereby the electromagnetic waves may be modulated.

Briefly stated, in the illustrated embodiments of our invention we provide-within a dielectric wave guide of the hollow-pipe type apparatus for establishing a region of charged electric particles, such as anl electron space charge region, Y associated with an aperture which is tuned to the frequency of the exciting means which establishes the electromagnetic waves l within the guide. The region of charged electric particles may be established by providing a source of electrons which constitutesa cathode and which cooperates with the wall comprising the tuned aperture. 'I'he magnitude of the space charge maybe controlled in a number of ways, one of which is the variation of the potential difference between the cathode and the wall comprising the slot; another way in which the space charge may be controlled is the provision of control means, such as electrostatic means orA grids, positioned between the cathode and the wall Variation of the density of the space charge controls the eifective dielectric constant of the Ymedium throughA which thev electromagnetic waves are propagated, thereby controlling the waves themselves. For `example, by control oi the density of the space charge, or, in other words, control of the number of charged electric particles within the vicinity of the resonant variation with distance from the axis of the guide.

AAlthough our invention is applicable to many types of waves, in the following description of our invention the H01 type will be referred to.

It is an object of our invention to. provide new and improved electric high frequency control systems.

It is another object of our invention to provide new and improved electronic control means for dielectric guides of the hollow-pipe type.

It is a further object of our invention to provide new and improved arrangements for controlling the propagation characteristics of dielectric wave guides by4 establishing a control region of charged electric particles, such as electrons or ions. in the vicinity of an aperture slot the propagation constants of the guide may be controlled at will, thereby modulating the electromagnetic waves which are transmitted.

Of course, the entire guide may be evacuated .and maintained at a sufficiently low pressure to permit ready control of the space charge density, or an isolated or sealed region may be established within the guide surrounding the slot and the associated structure which constitutes the anode, cathode, and control means.

\ For a better understanding of our invention, reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointedy out in the appended claims. Figs. 1 and 2 diagrammatically illustrate an'embodiment of our invention as applied to a dielectric wave guide tuned substantially to the frequency of the exciting means which establishes the electromagnetic waves within the guide.

having a rectangular cross section and which is provided with a metallic transverse wall includ- Y ing a resonant aperture or slot which is c ontrolled by means of a space charge established between a thermionic cathode and the transverse wall. Figs. 3 and 4 represent a further modification wherein the modulation of the electromagnetic waves is controlled by an electrostatic grid or grids positioned between the cathode structures and the wall which constitutes an anode for the electric discharge path; Figs. 5 and 6 represent views of a further modification including variations of the cathode structure and means for modulating the waves.

Prior to a detailed description of our invention, it is believed that it may be helpful to point out particularly certain general aspects concerningv the propagation of ultra high frequency electro magnetic waves through dielectric wave guides, with particular 'attention to dielectric wave guides having rectangular cross sections. There is a critical minimum frequency or cut-oil frequency for each dielectric guide, the value of which is determined by the dielectric constant of the medium within the guide through which the electromagnetic waves are propagated and the transverse dimensions of the guide. Below this value of critical frequency, the electromagnetic waves are rapidly attenuated and the energy thereof is not transmitted an appreciabler distance along the axis of the guide. Above the critical frequency, the electromagnetic waves are propagated with an attenuation and velocity determined by the propagation constant of the guide. This propagation constant P may be expressed as follows:

:a-I-i (1) which varies with-the transverse dimensions of the guide. When the excitation frequency is below the critical frequency, the expression (1) may still be used but now a and both become imaginary with the result that vdetermines theV .attenuation and determines the extent oi' wave action. Since below the critical frequency 2s is again much larger than a, the attenuation is very pronounced and the wave action is very small. Physically, this means that transmission of waves through the guide is virtually non-existent at frequencies below the cut-of! frequency.

Although our invention may be applied with equal facility to dielectric wave guides of various conflgurations, in the following discussion in order to present 4some fundamental considerations relative to the description of our invention, the fundamental aspects will be described with particular reference to dielectric wave guides havingv a rectangular cross section and wherein the height of the guide is a and the base is b.

The phase constant may be expressed:

M @n i V [UMH-(7) b :l (2) where u is the angular velocity of the wave propagated through the medium, (u=2ff), f is the frequency of the wave, m is the permeability of the medium and e1 is the dielectric constant of the medium. The quantities n and mere. of

4 course, the order and mode of the. particular wave being transmitted through the guide.

The critical frequency -fo may be defined as follows:

made# eil* e the order of the Wave becomes larger. Further- .more, it will be noted that as either Adimension a or b of the wave guide is decreased, the critical frequency increases. In addition, it should be noted that the critical frequency may also be decreased by increasing the value of the dielectric constant or by employing a material having a larger dielectric constant.

In order to simplify still further the presentation of the subject matter of our invention, it will be assumed that the dielectric is air and that the system is arranged for the transmission of an H01 type wave where the electric component of the eld is perpendicular to b, in which case the phase constant and critical frequency expressed by Equations 2 and 3, become:

eier-en* where c is the velocity of light in air./

The electromagnetic waves are propagated' through the guide; that is, theexpression for the progressive wave may be expressed as a function of the propagation constant and time. The electric intensity and the magnetic eld may be expressed as follows:

E=(real) Efe-52H4wt (7) H=(real) He-HM (8) ture or slot and wherein the eil'ective dielectric constant of the medium within the vicinity of the aperture is controlled by means of a region of charged particles, such as an' electron stream, thereby modulating the electromagnetic waves within the guide.

While in the specific description of our invention, we have chosen to describe the electric discharge means which produces the region of charged particles as being one which produces a stream or beam of electrons, it will be appreciated that we contemplate the provision of electric discharge means for establishing within the vicinity of the resonant slot or aperture a region of charged electric particles. For example, we may be employed.

Since it is not the purpose of the present de` scription to enter into a highly Atheoretical and rigorous analysis of the phenomena associated with apparatus embodying ourfinvention, it may be sumclentto state that the effective dielectric constant of the medium through which the electromagnetic waves are propagated'is a function of the diierence of the dielectric constant of the medium .with no charged particles present and a quantity which is directly proportional to the number of charged particles per unit volume, the square of the unit charge of each particle, and inversely proportional to the mass of each charge and some function of the frequency of the iield.

Referring now to Fig. 1 of the accompanying drawing, we have there illustrated our invention as applied to a dielectric Wave guide of the hollow-pipe type for controlling the transmission of ultra high frequency electromagnetic waves. For purposes of facilitating the description of our invention, We have chosen to illustrate the dielectric AWave guide as being of rectangular cross section comprising a top plate i and a Vbottom plate 2, preferably constructed of a highly conductive metal such as copper or brass. It will be understood that similar side walls t and t (Fig. 2) are also included to provide With end walls 5 and 6 a conning and directional chamber for the electromagnetic waves.

In order to establish within the wave guide electromagnetic Waves, We may employ exciting A electrode means. such'as a coaxial or concentric transmission line comprising an outer tubular conductor 'i and a conductor 8, the former of` Output electrode means may also be associl ated with the dielectric Wave guide and may be similar in construction and arrangement to the input electrode means, that is, may also 'comprise a concentric transmission line including a tubular Vconductor il conductively connected to the guide and an inner conductor it. If desired, boththe input and output electrode means may be provided with a seal, such as a vitreous seal,

. Where-it is not desired to employ within the main section of the guide an isolated or evacuation region of low pressure.

It should be understood that in place of ernploying output electrode means for extracting energy from the-guide, the end of the guide may be open to permit radiation of the propagated Waves into space. For example, the end of the guidel may be open and terminated in a ared horn (not shown) for radiation purposes.

s We employ with\in the dielectric wave guide a metallic wall II which is conductively connected to the top, bottom and sides of the guide' and which lies in a plane substantially transverse to the direction of propagation of the electromagnetic waves through the guide. The wall ii is designed to have a resonant aperture, such as an elongated slot I2, having an appreciable dimension transverse to the electric component of the H01 type wave transmitted through the guide. The aperture I2 maybe of rectangular shape having a height h and a principall dimension L (see Fig. 2).4 The dimensions oi the resonant slot AI2 may'be chosen so that substantially the entire voltagediflerence due to the electromagnetic waves within the guide appears across' the .where A is the wave length of the exciting means. For a more detaileddescription of the characteristics of the resonant aperture or slot, reierence may lbe hadto the copending patent application of Milan D. Fiske and J. M. Laferty,

Serial No. 458,422, filed September 15, 1942, and

ent application. The vector E represents the direction of the transverse orv electric component of the electrgmagnetic eld of the waves transmitted through the guide.

We provide means for establishing within ,the vicinity of the. resonant aperturev i2 a region of charged electric particles which may be an electron stream or beam to control the propagation of the electromagnetic waves. The region oi charged particles or the electron streamimay include a cathode comprising a thermionic filament I3 which cooperates with the wall Iii to provide an electric discharge path, the wall it constituting the anode. If desired, a similar cathode structure may be provided on the other side of the wallI i and may comprise a thermionic cathode It, in which case the wall II functions as an anode for both cathodes.

Whereit is desired to localize the evacuated region around the wall it or the slot I2, we may provide a sealed section .or region within the guide. The sealed region may be defined by dielectric Walls vIii and IB preferably constructed of a vitreous. material such as glass andwhich are sealed to the top, bottom and side Wall. Evacuation may be effected by providing a suitable glass tubulation( not shown) extending into the localized region and which after evacuation may be sealed od in the conventional manner.

A more complete understanding of our invention shown in Fig. 1 may be obtained by referring to the top cross-sectional View thereof illustrated in Fig. 2 where corresponding elements have been assigned like reference numerals. The thermionic cathodes I3 and I4 may be supported in spaced relation relative'to each other and to the slot I2 by means of rigid metallic conductors I12Il, inclusive, which are insulated from the side walls 3 and I by means of suitable vitreous or glass insulators 2I-24, respectively, which may be sealed to the metallic walls by employing an alloy including iron, nickel and cobalt.

The thermionic cathodes I3 and I4 may be energized from any suitable source of current connected between the metallic wave guidel through a` conductor 21. The other terminal of the source 26 is connected to the thermionic cathodes I2 and Il through the lead-in conductors I I and Il.

The operation ofthe embodiment of our inventionl illustrated in Figs. 1 and 2 will be explained first by considering the system when the potential dlii'erence between the cathodes I3 and il and the wall Il is such that no electrons iiow from cathodes I2 and Il to the wall Il. In view' of the discussion above. it will be understood that if the wave guide is excited at a frequency greater than the critical minimum frequency the electromagnetic waves will be propagated through the guide and will obtain a wave length ).g determined principally by the phase constant p.

As evidenced by Equation 2 discussed above, it will be understood that p is determined in a measure by the dielectric constant of the medium through which the waves are being transmitted.

Upon lchange of the potential diiference between the cathodes i3. Il and the wall Il to permit electron flow from the cathodes to the wall, there will be established a region of charged particles, that is a stream of electrons constituting a space charge which aifects. that is decreases. the magnitude of the eective dielectric constant of the region immediately surrounding the tuned aperture. Consequently.' the phase constant also decreases, thereby 'changing the wave length of the waves transmitted through the guide. The critical frequency of the waves transmitted through the wave guide is also changed. In this instance. however. the critical frequency is increased. If thechange in the.

effective dielectric constant is sufficiently great, it will be appreciated that the critical frequency may become Agreater than the frequency of the exciting means so that electromaginetic waves are not transmitted an appreciable distance beyond the wall Il; that is, the electromagnetic waves are substantially completely attenuated.

It is to be appreciated that in the systems which we contemplate, the variation in the effective dielectric constant of the medium within the guide may not be varied or changed to a value which e'ects this substantially complete attenuation, but may be varied or modulated within limits above those corresponding .to the minimum or critical frequency for the particular guide. That is, electromagnetic waves may be transmitted through the guide, the controlling effect being that obtained by modulating the waves so transmitted. v

As will be understood from the discussion above relative to the variation of the phase constant as a function of the effective dielectric constant of the guide, by controlling the magnitude or density of the charged particles a wave guide employing our invention mayv be used to phase modulate high frequency electromagnetic waves. For example, in the arrangement of Fig. 1 by controlling the density of the electrons in the discharge path within the vicinity of the resonant aperture I2, the phase of the electromagnetic waves received at the output electrode means comprising conductors! and I0 may be modulated relative to the voltage or excitation of the input electrode means. Furthermore. by con- 'charge paths provided by 8 trolling the length of the guide or the distance between the input and the output electrode means. frequency modulation may also be obtained.

As an additional matter, attention is directed to the fact that apparatus embodying the subject matter of our invention may be employed as a wave nlter inasmuch as the transverse wall including the resonant slot and the associated region of charged particles is highly selective to waves of a frequency determined by the design of the slot or to waves within that region, thereby reflecting waves of different frequency.

The arrow I shown in Fig. 2 represents the direction of the incident wave and the dotted arrow R represents the reflected waves. Arrow T indicates the transmitted waves through the guide.

Although we have illustrated a source of alter' nating current 26 as a means for controlling the potential difference between the wall Il and the cathodes I3 and Il. it will be appreciated that we may employ other means of a periodic nature, or intermittent nature, for controlling the propagation of electromagnetic waves through the guide and for effecting complete attenuation of the waves.

Figs. 3 and 4 diagrammatically illustrate a further modincation of our invention which may be applied to a dielectric wave guide and may constitute a portion of the arrangement shown in Fig. 1. In this modincation of our invention. the density of the charged particles, or the density of the space charge, is determined by control means which may be electrostatic control members or grids 2l and 29 which are positioned between the slot I2 and cathodes ll and 3| which may also be of the thermionic type. In this arrangement. the wall I I also serves as an anode. The lead lines for cathodes 3| and 2| and grids 28 and 29 are insulated from the side walls 3 andA I by means of glass insulators 32-35, inclusive. which are sealed to the side walls.

The density of the space charge and, hence, the propagation characteristics of the guide are controllable by means of the grids 28 and 29. The potential of t ese grids may be controlled. if desired, by Joint means such as a signal source 38 of alternating current which cyclically affects the potential of the grids with respect to the wall Il. If desired. a separate source of current may be employed for energizing the electric disthe :wall H and cathodes 3l andral. This source may comprise a battery 31 which impresses a positive 'potential on the walls of the guide and consequently impresses a positive potential on wall I I.

In operation. the embodiment of our invention shownin Figs. 3 and 4 may also be employed to modulate the waves transmitted through the guide and also may be employed to completely attenuate the waves by exciting grids 2l and in such a manner as to establish a space charge of sumcient density to decrease the eective dielectric constant of the medium surrounding the tuned aperture so that the frequency of the aperture is changed toa value less than the critical frequency.

Referring now to Figs. 5 and 6, there is illus- Vtrated a still further modification of the structure which may surround the tuned aperture to .control its characteristics and the wave propader 38 may be supported within the guide by means of a vitreous or glass insulator 40 which mayextend intothe cylinder 38 an appreciable distance at one end and which is supported at the other end by a-metallic collar 4| which may be welded or soldered to the side wall 3. At the other end the cylinder n may be supported by rigid conductors which extend through a suitable 9.41am I i tially to the frequency of said exciting means, and means comprising a thermionic means for establishing a space charge within the vicinity of said aperture to control the wave propagation characteristics of said chamber.

3. In combination, a chamber for conning and propagating electromagnetic waves. exciting v means for establishing electromagnetic waves within said chamber, a wall within s aid chamber lying in a plane substantially transverse to the direction of wave propagation through 'said chamber and comprising an aperture tuned substantially to the frequency of said exciting means, and a thermionic filament substantially parallel to the principal dimension of said aperture for establishing a space charge within the vicinity thereof for controlling .the wave propagation vitreous seal 42, the latter of which is maina tained or supported by a ilanged cylinder 43 which is welded or soldered to wall 4.

In this embodiment of -our invention, the space charge may be controlled by controlling the potential of cylinder 38 and may be effected by employing aconductor'44 which also extends through theinsulator 42 and is conductively attached to the surface of cylinder 38. 'I'he potential of cylinder 38 may be periodically, intermittently, or cyclically varied in response toa predetermined signal which may be derived from an alternating current source 45 which may be oi either high, low, or intermediate frequency.

The iilament 39 may be energized from a suitable source of current such as a battery 4B.

i similar cathode structure may be positioned on the other side of the wall il of the resonant structure and may comprise a metallic cylinder di and an associated filament orheating element dt. The potential ofthe cylinder 41 may also be controlled to control or vary the density of the space charge and may be varied in synchronism with the potential of cylinder 38. To effect this result, conductor 49 may be connected, in the manner illustrated, to conductor 4d and source d5.

While we have shown and described our invention as applied to particular systems embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from our invention, 'and we, therefore, aim in the appended claims to cover al1 such changes and modifications as fall within the true spirit and scope of our invention.

Whatwe claim as new and desire to secure by Letters Patent of the United States is:

l. In combination, a chamber for confining and propagating electromagnetic waves, 'exciting means for establishing electromagnetic waves within said chamber, a wail within said chamber lying in a plane substantially transverse to the direction of wave propagation through said chamber and comprisingv an aperture tuned substantially to the frequency of said excitingmeans, and means for producing a region of charged particles Within the vicinity of .said aperture to control the wave propagation characteristics of said chamber.

2. In combination, a chamber for confining and propagating electromagnetic waves, exciting means for establishing electromagnetic waves within said chamber, 'a wall within said chamber lying in a plane substantially transverse to the direction of wave propagation through said chamber and comprising an aperture tuned substancharacteristics of said chamber.

4. In combination, a chamber for confining and propagating electromagnetic waves, exciting means for establishing' eletromagnetic wave-s within said chamber, a wail within said chamber lying in a plane substantially transverse'to the direction of wavepropagation through said chamber and comprising an aperture tuned substantially to the frequency of said exciting meansf and a pair of thermionic filaments one'on each side of said aperture and extendingsubstantially parallel with the principal dimension thereof for establishinga space charge and for controlling the wave propagation characteristics of said chamber.

5. In combination, a dielectric Wave guide of the hollow-pipe type, means for exciting said wave guide at a frequency greater than the critical frequency and for establishing electromagnetic waves within said guide, a wail within said guide lying in a. plane substantially transverse to the direction of Wave propagation therethrough and comprising an aperture of appreciable'disinension tuned to the frequency vof the exciting electromagnetic Waves, and means comprising a filament extending substantially parallel with the principal dimension oi said aperture for establishing a space charge thereby controlling the Wave propagation zharacteristics of said guide. 4.

6. In combination, a dielectric wave guide of the hollow-pipe type, means for establishing within said guide electromagnetic waves of a frequency greater than the critical frequency of said guide, a wall within said guide lying in a plane substantially transverse of the direction of wave propagation through said guide and comprising an aperture'tuned substantially to the'frequency of said exciting Waves, and means :for producing a space charge Within the vicinity of said aperture to control the wave propagation characteristics of said guide.

'15in combination, a dielectric wave guide of the Vhollow-pipe type comprising a substantially conductive wall, exciting means -for exciting said guide at a frequency greater than the critical frequency and for establishing electromagnetic Waves within said guide, a wall within said guide lying in a plane substantially transverse ,to the direction of wave propagation therethrough and comprising an aperture of appreciable dimension tuned substantially to the frequency of said exciting means, and a pair of thermionic filaments extending substantially parallel with the principal dimension of said aperture for establishing a space charge and for controlling the wave propagation characteristics of said guide.

8. In combination, a dielectric wave guide of the hollow-pipe type, means for exciting said Wave guide at a frequency greater than the critical frequency and for establishing electromagnetic waves within said guide, a wall within said guide lying in a plane substantially transverse to the. direction of wave propagation therethrough and comprising an aperture of appreciable dimension tuned to the frequency of the exciting electromagnetic waves. means comprising a filamentary cathode within the vicinity of said aperture for establishing a space charge, and means for controlling the potential of said filament for modulating the waves transmitted through said guide.

9. In a system for transmitting electromagnetic 'waves through a dielectric wave guide which includes within the guide a resonant aperture tuned to the frequency at which the guide is excited, the method of controlling the transmission of said waves through said guide which comprises establishing a region of charged particles within the vicinity of said aperture and controlling the propagation of electromagnetic waves through said guide by establishing an electrostatic field between said guide and the means which produces the charged particles.

10. In combination, a dielectric wave guide of the hollow-pipe type comprising a metallic conning member, means for exciting said wave guide at a frequency greater than the critical frequency and for establishing electromagnetic waves within said guide, ametallic wall within said guide lying in a plane substantially transverse to the. direction of wave propagation therethrough and comprising an aperture of appreciable dimension tuned to the frequency of the exciting electromagnetic waves, means for establishing a space charge within the vicinity of said aperture and comprising a, filament within the vicinity of said aperture, said filament being electrically insulated from said confining member, and means connected between said confining wall and said filament for varying the potential difference between said filament and said confining member.

1'1. In 'a system for transmitting electromagnetic waves dielectrically through a metallic wave guide which comprises a transverse wall within the guide having an aperture tuned substantially to the exciting frequency of said guide, the

. method of modulating the electromagnetic waves transmitted therethrough which comprises establishing a space charge within the vicinity of said aperture and modulating the waves by varying the density of said space charge in accordance with a modulating signal.

12. In combination, a dielectric wave guide of the hollow-pipe type, means for exciting said wave guide at a frequency greater than the critical frequency and .for establishing electromagnetic f waves within said guide, a wall within said guide lying in a plane substantially transverse to the direction of wave propagation therethrough and comprising an aperture of appreciable dimension tuned to the frequency of' the exciting electromagnetic waves, a pair of laments positioned on each side of said aperture for establishing a space charge, and means for controlling the potential of said laments relative to said guide for modulating the electromagnetic waves transmitted therethrough.

13. In combination, a dielectric wave guide of the hollow-pipe type.V exciting means for establishing within said guide electromagnetic waves of a frequency greater than the critical frequency of said guide, a wall within said guide lying in a plane substantially transverse to the direction of wave propagation therethrough and comprising an aperture tuned substantially to the frequency of said-exciting means, means for establishing a space charge within the vicinity of said aperture comprising a filamentary cathode which constitutes with said wall a discharge path, and electrostatic control means positioned between said Wall and said cathode for controlling the magmtude of-said space charge.

14. In combination, a dielectric wave guide of the hollow-pipe type, exciting means for establishing within said guide electromagnetic waves of a frequency greater than the critical frequency of said guide, a wall within said guide lying in a plane substantially transverse to the direction of wave propagation therethrough and comprising an aperture tuned substantiallyto the frequency of said exciting means, means for establishing a space charge within the vicinity of said aperture the hollow-pipe type, exciting means for establishing within said guide electromagnetic waves of a frequency greater than the critical frequency of said guide, a wall within said guide lying in a plane substantially transverse to the direction of wave propagation therethrough and comprising an aperture tuned substantially to the frequency of said exciting means, means for establishing a space charge within the vicinity of said aperture comprising a'illamentary cathode which constitutes with said wall a discharge path, a grid positioned between said wall and said cathode, and means for controlling the potential of said grid for modulating the electromagnetic waves transmitted through said guide.

16. In combination, a dielectric wave guide of the hollow-pipe type, exciting means for establishing within said guide electromagnetic waves of a frequency greater than the critical frequency of said guide, a wallA within said guide lying in a plane substantially transverse to the direction of wave propagation therethrough and comprising an aperturetuned substantially to the frequency of said exciting means, a. pair of filamentary cathodes mounted on each side of said aperture and constituting with said wall a pair of electric discharge paths, and a pair of grids each positioned between. said wall'and a different one of said cathodes for controlling the magnitude of the space charge.

17. In combination, a dielectric wave guide of the hollow-pipe type, exciting means for establishing electromagnetic waves within said guide f controlling the potential of said cylinder to control the magnitude of the space charge.

18. In combination, a dielectric wave guide of the hollow-pipe type, input exciting means for establishing electromagnetic waves within said guide of a frequency greater than the critical frequency thereof, a wall -within said guide lying in a plane substantially transverse to the direction of wave propagationtherethrough and comprising an aperture tuned substantially to the fre-` V the hollow-pipe type and filtering means selectively responsive to an electromagnetic wave of predetermined frequency comprising a wall within said guide lying in a plane substantially transverse to the direction of wave propagation therethrough and having an aperture tunedrsubstantially to said frequency and means associated with said aperture for establishing a region of charged electric particles. y

20. In combination, a' dielectric wave guide of the hollow-pipe type, filtering means for controlling the selectivity of said guide comprising a wall lying in a plane substantially transverse to the direction of wave propagation and having therein an aperture tuned to a resonance frequency, and means comprising an electric discharge path for .varying saidlresonance frequency for controlling Y the wave propagating characteristics of said aperture.

the hollow-pipe type.` and means for controlling the wave propagating characteristics of said guide comprising a wall lying in a plane substantially transverse to the" direction of wave propagation therethrough and having therein an aperture tuned to a resonance frequency, and means associated with said aperture-.for establishing within the vicinity thereof a region of charged electric particles. Y v

22. In combination, a dielectric wave guide of the hollow-pipe type, and means for controlling the wave propagating characteristics of said guide comprising a conductive member havingtherein an aperture tuned to a resonance frequency, said member having va phase extension in the direction A of wave propagation through said guide which is a small portion of a wavelength at said resonance frequency, and means associated with.

MILAN D. FISKE. CHAUNCEY G. SUITS.

2l. In combination, 4a dielectric waveguide of' Disclaimer 2,413,963.-Mz'lcm D. Fz'sce and @hmm/eey G. Suits, Schenectady, N. Y. ULTRA HIGH FREQUENCY CONTROL SYSTEM. Patent dated Jan. 7, 1947. Disclaimer filed June 14, 1951, by the assignee, General Electric Oompa/ny.

Hereby enters this disclaimer to claims 1, 6, 9, 19, 20, 21, and 22 of said, patent. [Oycial Gtzette Awgwst 7, 1.951.] 

